The present invention relates to underwater illuminating lamps having over-temperature protection and, more particularly, to a submersible lamp structure designed to provide underwater illumination for swimming pools and the like which is protected against over-temperature operation when the level of the water drops below a predetermined level.
Various lamps and lamp housing assemblies are known for providing underwater illumination for swimming pools, fountains, and the like. Some of these designs depend upon the presence of the surrounding water to absorb the excess heat energy developed by the lamp filament and thereby maintain the lamp and its housing in a preferred temperature range. However, when the level of the surrounding, cooling water inadvertently drops below the level of the operating lamp, the heat energy which would normally be transferred to the surrounding water causes the temperature of the lamp and its housing to increase and thereby cause an over-temperature condition. Repeated or extended over-temperature operation can materially reduce the operating life of the lamp filament; cause distortion and stress in the various parts of the lamp and lamp housing; and cause any plastic parts, including plastic sealing gaskets, structural elements, and electrical insulating parts, to distort, crack, or embrittle. Should the level of the cooling water be restored while the lamp is in an over-temperature condition, the resultant thermal shock can cause further material and structural deterioration, stress, and damage to the lamp and its housing.
A problem which must be considered in providing low-water protection for normally submerged lamps is that the temperature of the water and that of the ambient air, in those climates which have a small diurnal temperature variation over an extended period, can become approximately the same such that conventional temperature sensors may not be able to quickly discriminate between the presence or absence of the cooling water based on temperature alone.